Electrical resistance elements durable at high temperatures and proof against chemical action, and process of making same



Patented Dec. 10, 1946 ELECTRICAL RESISTANCE ELEMENTS DU- RABLE AT HIGH TEMPERATURES AND. PROOF AGAINST CHEMICAL ACTION, AND PROCESS OF MAKING SAME Axel Richard Wejnarth, Stockholm, Sweden No Drawing. Original application November 27,

1943, Serial No. 512,054. Divided and this application September 24, 1945, Serial No. 618,420. In Sweden October 20, 1942 7 Claims.

Resistance rods of silicon carbide have earlier been manufactured. However, in the said rods it hasbeen necessary to take into consideration a decreasing resistance at rising temperature. In the manufacture of rods of the kind mentioned there are used a binding medium and an addition of free silicon, said component facilitating the sintering and, when used in an appropriate quantity, at the same time imparting to the rods a suitable electric conductivity. It has proved on one hand that such resistance elements are able to endure an annealing temperature of about 1400 C. only, after whichrtheir conductivity is changed and the rods are destroyed, and on the other hand that they are very easily deteriorated in respect of durability and electric conductivity when brought into contact with particles from furnace lining, and by the action of surrounding metallic vapors or oxides, sulphides which may have formed, and so on.

In the manufacture of resistance elements of the kind described by sintering silicon carbide that may have been pressed and having different fineness of grain other suitable components may be added either prior to the sintering process or be allowed to be formed during the said process in order to regulate in a suitable way the electric conductivity of the resistance element at difierent temperatures, increase its temperature of use and improve its resistance to ceramic stuffs, metals, metallic oxides or the like.

added metal or metal from the added metal compound, and then heating the mixture to sinter- I ing at desired temperature. Instead of such ab- It is possible to use for such purpose carbides,

nitrides, silicides and borides of difllcultly fusible metals such as Be, Mo, W, Ti, V and Cr. For certain purposes it has proved suitable to have the mass contain also nitrides, silicides or borides of y the less difficultly fusible metals Mn, Fe, Ni and The said components having diiferent electrical conductivity, which may vary with the temperature and in a certain component even may assume a positive as well as a negative coefficient of temperature. within a certain range of temperature, there is a possibility of regulating, by means of one or more such components, the electric conductivity of the resistance element in a suitable 'way in relation to the silicon carbide contained in the mass.

According to the invention there: may be added another carbide or silicide, but it is also possible to form a certain carbide and/or silicide by adding to the silicon carbide, before or during the sintering process, a suitable quantity of one or'more metals or metal compound capable of reacting with silicon carbide while binding the sorbation of metal in the grate of the silicon carbide it is possible to form the desired compounds and/or mixtures of carbides and/or silicides by adding to the silicon carbide a mixture of metal or metal compound with a suitable quantity of carbon or silicon, preferably in a suitable mixing proportion. The silicides having, as a rule, lower melting points than the corresponding carbides and thus, usually already at rather low contents, causing an upper limitation of the temperature of the resistance elementit appears a general wish to try to form more carbide than silicide.

Analogously it is possible either to add to the silicon carbide one or more nitrides, or borides, or to form the same, before or during the sinthe respective compounds that may occur in connection with the manufacture of. electrical resistance elements durable at high temperatures and proof against chemical action cannot be specified, but by way of example the following may be stated. In testing the relevant circumstances it has appeared, for example, that manganese, chromium and Wolfram form lower meltingsilicides than carbides, but that the said com-J j pounds of chromium are more durable than those of manganese and wolfram but. at the'same time more easily conducting. A suitable combination of wolfr'am or of manganese, or of both of them, v .with silicon carbide containing chromium results in a lower averageelectric conductivity and, all according to the testing conditions, composed carbides and/or silicides formmore durable resist ance elements than an element with silicon carbide containing, for example, Wolfram only. The

' gains-7s The invention relates more particularly to rodshaped elements of various design and cross section, but is not restricted thereto. A product of the proposed composition sintered in some way or other can be crushed and used as a heat resisting medium in the form of grains or powder, and

also in such state form resistance elements. Such a material can be applied to resistance elements of carbon'or graphite as a protecting coatin which in itself forms a resistance element.

Nor is the invention restricted to elements consisting of the combinationsof components set forth in the following claims but also all other possible combinations of two or more of the components with each other fall within the scope of the invention.

This application is a division of application Serial Number 512,054, filed November 27, 1943,

component silicon carbide and, moreover, in smaller quantity, at least one compound, belonging to the group of chromium carbide, chromium nitride, chromium silicide and chromium boride, and at least one compound, belonging to the group of titanium carbide, titanium nitride, ti-

- tanium'silicide and titanium boride.

2. Electrical resistance element according to claim '1, the mass containing also at least one compound, belonging to the group of manganese nitride, manganesesili'cide and manganese b0- ride. 1 3. Electrical resistance element according to claim 1, the mass containing also at least one compound, belonging to the group of iron nitride, iron silicide and iron boride.

4. Electrical resistance element according 'to claim 1, the mass containing also at least one compound, belonging toythe group of nickel nitride, nickel silicide and nickel boride,

5. Electrical resistance element according to claim 1, the mass containing also at least one compound, belonging to the gmup of cobalt nitride, cobalt silicide and cobalt boride.

entitled Process of manufacturing resistance 1 v elements durable at high temperature and proof against chemical action.

Having now described my invention, what I claim as new and desire to secure by Letters Patent is; i

1. Electrical resistance element durable at high temperature and proot'against chemical action,

consisting of a sintered mass, containing as main 6. A process of making electrical resistance elements according to claiml, adding to the silicon carbide, prior to the sintering, the compounds desired to be included in the finished product.

' be included in 7. A process of making electrical resistance elements according to claim 1, adding to the silicon carbide components of the kind to form, durin the sintering process, the compounds desired to the finished product; AXEL RICHARD WEINARTH. 

